diff --git a/src/backend/access/heap/visibilitymap.c b/src/backend/access/heap/visibilitymap.c
index 3047bd46def..e21b96281a6 100644
--- a/src/backend/access/heap/visibilitymap.c
+++ b/src/backend/access/heap/visibilitymap.c
@@ -116,6 +116,8 @@
 
 /* Mapping from heap block number to the right bit in the visibility map */
 #define HEAPBLK_TO_MAPBLOCK(x) ((x) / HEAPBLOCKS_PER_PAGE)
+#define HEAPBLK_TO_MAPBLOCK_LIMIT(x) \
+	(((x) + HEAPBLOCKS_PER_PAGE - 1) / HEAPBLOCKS_PER_PAGE)
 #define HEAPBLK_TO_MAPBYTE(x) (((x) % HEAPBLOCKS_PER_PAGE) / HEAPBLOCKS_PER_BYTE)
 #define HEAPBLK_TO_OFFSET(x) (((x) % HEAPBLOCKS_PER_BYTE) * BITS_PER_HEAPBLOCK)
 
@@ -600,6 +602,21 @@ visibilitymap_prepare_truncate(Relation rel, BlockNumber nheapblocks)
 	return newnblocks;
 }
 
+/*
+ *	visibilitymap_truncation_length -
+ *			compute truncation length for visibility map
+ *
+ * Given a proposed truncation length for the main fork, compute the
+ * correct truncation length for the visibility map. Should return the
+ * same answer as visibilitymap_prepare_truncate(), but without modifying
+ * anything.
+ */
+BlockNumber
+visibilitymap_truncation_length(BlockNumber nheapblocks)
+{
+	return HEAPBLK_TO_MAPBLOCK_LIMIT(nheapblocks);
+}
+
 /*
  * Read a visibility map page.
  *
diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index 742137edad6..e1aa102f41d 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -23,6 +23,7 @@
 #include "postgres.h"
 
 #include "access/timeline.h"
+#include "access/visibilitymap.h"
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
 #include "access/xlogrecovery.h"
@@ -1351,7 +1352,8 @@ SummarizeSmgrRecord(XLogReaderState *xlogreader, BlockRefTable *brtab)
 									   MAIN_FORKNUM, xlrec->blkno);
 		if ((xlrec->flags & SMGR_TRUNCATE_VM) != 0)
 			BlockRefTableSetLimitBlock(brtab, &xlrec->rlocator,
-									   VISIBILITYMAP_FORKNUM, xlrec->blkno);
+									   VISIBILITYMAP_FORKNUM,
+									   visibilitymap_truncation_length(xlrec->blkno));
 	}
 }
 
diff --git a/src/bin/pg_combinebackup/t/011_ib_truncation.pl b/src/bin/pg_combinebackup/t/011_ib_truncation.pl
index 47d84434452..c5e0124c04d 100644
--- a/src/bin/pg_combinebackup/t/011_ib_truncation.pl
+++ b/src/bin/pg_combinebackup/t/011_ib_truncation.pl
@@ -1,7 +1,8 @@
 # Copyright (c) 2025-2026, PostgreSQL Global Development Group
 #
-# This test aims to validate that the calculated truncation block never exceeds
-# the segment size.
+# This test aims to validate two things: (1) that the calculated truncation
+# block never exceeds the segment size and (2) that the correct limit block
+# length is calculated for the VM fork.
 
 use strict;
 use warnings FATAL => 'all';
@@ -39,7 +40,7 @@ $primary->safe_psql(
     CREATE TABLE t (
         id int,
         data text STORAGE PLAIN
-    );
+    ) WITH (autovacuum_enabled = false);
 });
 
 # The tuple size should be enough to prevent two tuples from being on the same
@@ -83,6 +84,23 @@ cmp_ok($t_blocks, '>', $target_blocks,
 $primary->backup('incr',
 	backup_options => [ '--incremental', "$full_backup/backup_manifest" ]);
 
+# We used to have a bug where the wrong limit block was calculated for the
+# VM fork, so verify that the WAL summary records the correct VM fork
+# truncation limit. We can't just check whether the restored VM fork is
+# the right size on disk, because it's so small that the incremental backup
+# code will send the entire file.
+my $relfilenode = $primary->safe_psql('postgres',
+	"SELECT pg_relation_filenode('t');");
+my $vm_limits = $primary->safe_psql('postgres',
+	"SELECT string_agg(relblocknumber::text, ',')
+	   FROM pg_available_wal_summaries() s,
+	        pg_wal_summary_contents(s.tli, s.start_lsn, s.end_lsn) c
+	  WHERE c.relfilenode = $relfilenode
+	    AND c.relforknumber = 2
+	    AND c.is_limit_block;");
+is($vm_limits, '1',
+	'WAL summary has correct VM fork truncation limit');
+
 # Combine full and incremental backups.  Before the fix, this failed because
 # the INCREMENTAL file header contained an incorrect truncation_block value.
 my $restored = PostgreSQL::Test::Cluster->new('node2');
diff --git a/src/include/access/visibilitymap.h b/src/include/access/visibilitymap.h
index a0166c5b410..52cde56be86 100644
--- a/src/include/access/visibilitymap.h
+++ b/src/include/access/visibilitymap.h
@@ -45,5 +45,6 @@ extern uint8 visibilitymap_get_status(Relation rel, BlockNumber heapBlk, Buffer
 extern void visibilitymap_count(Relation rel, BlockNumber *all_visible, BlockNumber *all_frozen);
 extern BlockNumber visibilitymap_prepare_truncate(Relation rel,
 												  BlockNumber nheapblocks);
+extern BlockNumber visibilitymap_truncation_length(BlockNumber nheapblocks);
 
 #endif							/* VISIBILITYMAP_H */